Method for making titanium boride from phosphates



METHQD FOR MAKING TITANIUM BORIDE FROM PHOSPHATES Leif Aagaard, Plainfield, and Helmnt Espenschied, Me-

tuchen, N.J., assignors to National Lead Company, New York, N .Y., a corporation of New Jersey No Drawing. Application July 10, 1953 Serial No. 367,360

2 Claims. (Cl. 23-404) The present invention relates in general to refractory metal compounds and more particularly to titanium compounds of boron, and to an improved method for making the same.

Heretofore, refractory metal compounds of carbon, boron, zirconium and the like, sometimes referred to hereinafter as metalloids, have been prepared with a modicum of success by heating dry mixtures of a refractory metal oxide, such as for example calcined titanium dioxide or zirconium oxide, carbon and/ or an oxidic compound of boron, to form the refractory metal compound. However, prior methods have had to contend with the probiem of obtaining intimate and permanent contact between the inherently coarse metal oxide particles, and the carbon particles which, due to their fineness, tend to separate out from the mixture during reaction. In attempting to overcome this difiiculty, prior technicians have resorted to pelletizing the mixtures and then heating the pellets at temperatures from 2000 C. to 2500 C. The resulting product is a hard sintered mass of material which must be subsequently broken up into smaller particles and ground. However, such products can be ground mechanically to form a finely divided powder only with great difficulty due to the abrasiveness and hardness of the compositions. Hence, even the ground material is relatively coarse, the smallest particle size being about 80 microns. Moreover, the purity and toughness of this product is often impaired by a high percentage of graphite which is formed from the carbon at the high sintering temperature used. Although these relatively coarse products have been used in the field of powder metallurgy, the impurity and coarse granular nature of the material has impaired its usefulness. There is, therefore, no direct and commercially practicable method for producing finely divided relatively pure refractory metal compounds of boron and the like without recourse to grinding and milling operations.

An object, therefore, of the present invention is to provide an improved method for making refractory metal compounds of boron which is economical, which mav be carried out at relatively low temperatures and which is p oductive directly of a relatively pure finely divided product.

A further object of the invention is to provide a superior method for forming a mixture of carbon and a refractory metal compound wherein the carbon particles are maintained in intimate contact with the refractory metal compound.

A still further object of the invention is to provide substantially pure finely divided particles of titanium boride.

These and other objects will become apparent from the following more complete description of the instant invention.

The ten finely divided as used herein with reference to the size of the titanium boride particles formed directly by the process of this invention shall be understood nite States Patent 2,929,685 Patented Mar. 22, 1960 to mean that the effective sizes of the from 1 to microns.

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particles may vary In its broadest aspects the present invention relates to new and improved compounds of titanium boride; and to an improved method for making said compounds which comprises forming an intimate mixture of a'titanium phosphate, carbon, and boric acid, and then heating the mixture in an inert atmosphere at a temperature of from 1100 C. and higher until reaction is completed, generally at about 1600 C., to produce a finely divided titaniumboride.

In carrying out the invention it was discovered that the successful production of substantially pure finely divided titanium boride is dependent, in large measure, upon achieving an intimate mixture of the carbon and titanium components. As pointed out above, due to the coarseness of calcined oxides of titanium, as compared to the particle size of lamp black, it is impossible to form and maintain an intimate mixture of calcined titanium dioxide and finely divided carbon. However, the instant invention embraces the discovery that the problem of forming intimate mixtures of titanium and carbon can be effectively solved by providing the titanium component in the form 'of a titanium phosphate prepared of this invention may be titania metahydrate or titania orthohydrate and is preferably an untreated hydrate which occurs as an intermediate product in the production'of titanium dioxide pigment and which is generally referred to in the art as pulp. This untreated titania hydrate, or pulp, comprises particles, i.e. crystalloids or groups of crystalloids, the effective sizes of which may vary from .05 to 0.2 micron. Since the untreated pulp is usually formed by hydrolyzing an acid solution of titaniferous ore, the untreated pulp will contain or be combined with about 10% sulfuric or hydrochloric acid depending on the kind of acid solution used, and although the presence of the acid in the hydrate is not known to have a deleterious effect on the process or product of the invention, it is within the purview of the invention to remove the acid fraction from the hydrate by any of the techniques well known to the art of pigment manufacturing.

In achieving the objects of this invention it was discovered that when finely divided carbon is mixed with a titanium phosphate and boric acid, the particles of carbon are not only thoroughly and completely dispersed throughout the mixture but that the fine particle sizes greatly enhance the reactivity thereof such that when dried, the mixture may be calcined at relatively low temperatures to produce a substantially pure finely divided titanium boride.

With respect to the carbon used in the mixture of materials, a finely divided carbon, such as lamp black or oil burner soot, is suitable, the unit particles of which have an effective size of from about .01 to .05 micron. It is also within the purview of the invention to use a hydrophilic carbon, that is to say a carbon which has been treated with a suitable wetting agent, as for example one of the polyethylene glycol type, to insure dispersion of the carbon particles in an aqueous medium; or a wetting agent may be added to the admixed titanium phosphate carbon and boric acid.

In carrying out the process of this invention for the preparation of titanium boride, the carbon and boric acid may be admixed with the titanium phosphate in either of two ways. One way is to form the titanium phosphate first by mixing an aqueous slurry of titania hydrate with phosphoric acid in substantially stoichiometric amounts, partially drying the'mixture and then heating the dried mixture to form the pyrophosphate having the formula vert substantially all of the titanium values inthe mixture to Ititanium boride. After thoroughlycmixing the drypowders in a mortar or other suitablemeans, the mixtureis transferred directly 'to calcining. means, such asifor example an induction furnace or a rotating kiln capable of maintaining the temperatures required for calcining, the powdered material. The material is calcined at temperatures of from about 1100 C. to as high as about 1600 C. for from about 2 to 4 hours. ,Since it is essential to .the production of a relatively pure product that the .calcinirig treatment he carried out in an inert atmosphere, an atmosphere of argon is maintained within the calcining means throughoutthe calcination of the powdered material. g

The oxidic compound of boron may be added as ,boric oxide or preferably as boric acid powder.

Thereaction between the titanium pyrophosphate, carbon and boric acid during calcination may be represented by the following equation:

' I TiP -B O +10C=TiB +1OCO+2l wherein '1. mol of titaniumdioxide added in the form of titanium pyrophosphate reacts with 1 mol of boron oxide added in the form of boric acid ani 10 mols of carbon to produce 1 mol of titanium boride, 1O mols of carbon monoxide and 2 mols ofphosphorus. The latter may be recovered, converted to phosphoric acid and recycled, thereby insuring an efficient and highly economi- V cal operation.

Since, boric acid is somewhat volatile with water vapor,-

it is desirable to add substantially 10% or higher excess boric acid over the, theoretical amount, any excess boric acid being 'eiiectively removed by simple washing of the calcined product. I

As an alternative method'of mixing the carbon, boron and titanium values, a predetermined amount of carbon, preferably a hydrophilic carbon, which is miscible in an aqueous medium, is added to a mixture of phosphoric acid and aqueous titania hydrate slurry and the ingredients thoroughly mixed 'by agitation after which the mixture may be partially dried by heating at relatively low temperatures, as for example from 150 to 250 C.

1 titanium metalloids of boron may be produced in an' The dry or partially dried mixture is then broken up to provide afine'powder to which boric acid is added and the admixture calcined in the manner hereinabove described to form titanium boride.

' The calcined product is a finely divided powder of high purity, the unit particles comprising from 67% to 68% titanium and from 29% to 31% boron as compared to the theoretical amounts of 69% and 31% respectively for pure titanium boride. The crystalline structure of the unit particles comprises essentially substantially hexagonal plates of from 3 to 15 microns size. When higher calcining temperatures are used,'the calcining time is decreased-and the effective size of the particles may be less than 5 microns.

To further illustrate the invention, the following ex-- ample is given:

Example I 12 parts carbon black was added 12.4 parts by weight of boric acid powder. The mixture was thoroughly Worked for a sufiicient length of time to form an intimate mixture of the. materials whereupon the mixture was introduced into an induction furnace and calcined at a temperature of about 1500JC. for 2 hours in an atmosphere of argon. f a

The resulting product comprmised a finely divided powder which analyzed 68% titanium and 30% boronand had an effective particle size of from 1 to 5 microns.

In accordance with the improved process of this invention, metalloids of refractory metals and in particular 'efiicient and economical manner and from relatively inexpensive source materials. Moreover, the temperatures employed are relatively low, thereby precluding sintering and the formation of relatively large size particles, the calcining temperature for titanium boride being from about 1100 C. to about .1500 C. ,Further, the finely divided product of this invention has an effective particlel size ranging from 1 to 50 microns, but mostly of from 1 to 15 microns, is quite free of free 'carbon,,occluded graphite or other foreign'materials and hence is ideally suited for use in powder metallurgy, as abrasives, and in the production of cutting tool alloys and high temperature resistant alloys suitable for use in the manufacture of gas turbine blades.

While this invention has been described and illustrated by the examples shown, it is not intended to be strictly limited thereto, and other variations and modifications may be employed within the scope of the following claims. v Iclaim: f

1. Method for the production. of finely divided titanium boride which comprises: forming an intimate mixture oftitanium pyrophosphate, carbon and an oxidic compound of boron; said titanium pyrophosphate, carbon and an oxidic compoundof boron beingpresent in at least stoichiometric amounts, in said mixture; and heating said mixture at a temperature of from about 1100 C. to about 1600 C. in an atmosphere of'argon to calcine said mixture and .produce titanium boride havreaction between said materials, and in an atmosphere of argon to calcine said mixture and produce titanium boride having a particle size from about 1 micron to about 50 microns,

References Cited in the file of this patent FOREIGN PATENTS 14,124 Great Britain Nov. 17, 1900 OTHER REFERENCES Thorne et al.: Fritz Ephraim Inorganic Chemistry," 4th edition, 1943, page 849.

Barksdale: Titanium, 1949, page 87. 

1. METHOD FOR THE PRODUCTION OF FINLEY DIVIDED TITAMIUM BORIDE WHICH COMPRISES: FORMING AN INTIMATE MIXTURE OF TITANIUM PYROPHOSPHATE, CARBON AND AN OXIDIC COMPOUND OF BORON, SAID TITANIUM PYROPHOSPHATE, CARBON AND AN OXIDE COMPOUND OF BORON BEING PRESENT IN AT LEAST STOICHIOMETRIC AMOUNTS IN SAID MIXTURE, AND HEATING SAID MIXTURE AT A TEMPERATURE OF FROM ABOUT 1100* C. TO ABOUT 1600*C. IN AN ATMOSPHERE OF ARGON TO CALCINE SAID MIXTURE AND PRODUCE TITANIUM BORIDE HAVING A PARTICLE SIZE FROM ABOUT 1 MICRON TO ABOUT 50 MICRONS. 